Synchronous machine with common motor/generator exciter stage

ABSTRACT

A synchronous machine ( 100 ) has a frame ( 110 ), a shaft ( 115 ), a main section ( 120 ), and an exciter section ( 125 ). The main section ( 120 ) has a stator winding ( 130 ) which is mounted on the frame, and a rotor winding ( 135 ) which is mounted on the shaft. The exciter section has a transformer ( 140 ) and a rectifier ( 145 ). The transformer has a primary winding ( 140 A) mounted on the frame and a secondary winding ( 140 B) mounted on the shaft. The rectifier is mounted on the shaft and rectifies an output of the secondary winding to provide a rectified output to the rotor. A control unit ( 170 ) provides a high-frequency control signal to the primary winding. This signal is magnetically coupled to the secondary winding, rectified, and then applied to the rotor to control the operation of the synchronous machine.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of co-pending U.S. application Ser. No.14/498,186, entitled “Synchronous Machine With Common Motor/GeneratorExciter Stage” and filed on Sep. 26, 2014. The aforementioned relatedpatent application is herein incorporated by reference in its entirety.

BACKGROUND

A synchronous machine is an electric machine which can be operated aseither a synchronous motor (synchronous motor mode) or a synchronousgenerator (synchronous generator mode). Conventionally, a synchronousmachine has two separate and independent exciter field windings. Also,conventionally, two separate and independent control units have beenused, one control unit for the exciter field winding for the synchronousmotor mode and another control unit for the exciter field winding forthe synchronous generator mode. The use of two exciter field windingsand two control units make the synchronous machine and the system inwhich it is being used more complicated, heavier, and less reliable. Thedual excitation components of a conventional synchronous machine mayrepresent 20 to 30% of the total volume and weight of the synchronousmachine. Some conventional systems use only a single, reconfigurablefield winding, but still use two separate and independent control units,which then use switches or contactors to connect the appropriate controlunit to the field winding. Dual field windings, dual control units,and/or switches and/or contactors add cost, weight, volume, andcomplexity to the system, and adversely affect the overall reliabilityof the system. U.S. Pat. No. 5,770,909 to Rosen et al., herebyincorporated in its entirety herein by reference, discloses asynchronous motor-generator system which uses a rotary transformer.

Conventional synchronous machines also use a low frequency excitationcurrent and large field windings are used to avoid energy losses. Theselarge field windings substantially increase the amount and weight of theexpensive copper used in the windings. Further, with the conventionallow frequency excitation current, the back electromotive force generatedin the field windings is significantly affected by the rotor speed, andthis can cause stability problems during the startup process.

SUMMARY OF THE DISCLOSURE

A synchronous machine is disclosed which is operable as either asynchronous motor or a synchronous generator. The synchronous machinehas a frame, a shaft, a main section, and an exciter section. The mainsection has a stator (a stationary winding, which may be an armaturewinding) which is mounted on the frame, and a rotor (a rotating winding,which may be a field winding) which is mounted on the shaft, the statorand the rotor being magnetically coupled to each other. The excitersection has a transformer and a rectifier. The transformer has a primarywinding secured to the frame and a secondary winding secured to theshaft. The primary and secondary windings are spaced apart from, andmagnetically coupled to, each other. The rectifier is electricallyconnected to the secondary winding, is mechanically connected to therotor, and rectifies an output of the secondary winding to provide arectified output to the rotor. The primary winding and the secondarywinding of the transformer are each in the shape of a disk.

A control unit provides a control signal to the primary winding tocontrol the operation of the synchronous machine.

In one embodiment, the primary winding has an interior radius and thedisk defines a plane which is perpendicular to the shaft, and thesecondary winding has an exterior radius, which is smaller than theinterior radius, so the secondary winding is positioned within theprimary winding.

In another embodiment, the primary winding is mounted to the frame at anend of the shaft, the disk of the primary winding defining a first planewhich is perpendicular to the shaft, and the secondary winding issecured to the shaft near an end of the shaft, the disk of the secondarywinding defining a second plane which is perpendicular to the shaft, thesecond plane being parallel to and spaced apart from the first plane,the shaft does not penetrate the first plane, and the shaft has achannel in which electrical conductors are placed to connect therectifier with at least one of the secondary winding or the rotor.

A method of manufacturing a synchronous machine operable as either asynchronous motor or a synchronous generator is also disclosed. Themethod includes providing a frame, mounting a stator on the frame,providing a shaft which extends from at least one end of the frame,mounting a rotor on the shaft, mounting a primary winding of atransformer on the frame, mounting a secondary winding of thetransformer on the shaft, spaced apart from, but magnetically connectedto, the primary winding, securing a rectifier to the shaft, andelectrically connecting an input of the rectifier to the secondarywinding and an output of the rectifier to the rotor. Either thesecondary winding is mounted within the primary winding, such that theyare in the same plane, or the secondary winding is mounted facing theprimary winding, so that they are in different planes. A channel isprovided in the shaft so that electrical conductors may be run from therectifier to the secondary winding and/or the rotor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of an exemplary synchronous machine.

FIG. 2 is a diagram illustrating one exemplary embodiment of thesynchronous machine.

FIG. 3 is a diagram illustrating another exemplary embodiment of thesynchronous machine.

DETAILED DESCRIPTION

FIG. 1 is a diagram of an exemplary synchronous machine 100. Thesynchronous machine 100 has a frame 110, a shaft 115, a main section120, and an exciter section 125. The main section 120 has a stator 130(a stationary winding, which may be an armature winding) which ismounted on the frame, and a rotor 135 (a rotating winding, which may bea field winding) which is mounted on the shaft 115. Part of or all ofthe frame 110 may be part of, or may be distinct from, a casing whichencloses the synchronous machine 100.

The exciter section 125 has a transformer 140 and a rectifier 145. Thetransformer 140 has a primary winding 140A mounted on the frame 110 anda secondary winding 140B mounted on the shaft 115. The secondary winding140B is spaced apart from, and is magnetically coupled to, the primarywinding 140A. The rectifier 145 is electrically connected by a pluralityof electrical conductors 137 to the secondary winding 140B, iselectrically connected by a plurality of electrical conductors 142 tothe rotor 135, and rectifies an output of the secondary winding 1408 toprovide a rectified output to the rotor 135. For convenience and brevityof expression, “electrical conductors”, and a “plurality of electricalconductors”, are sometimes referred to herein simply as “conductors”.The rectifier 145 is secured to the shaft 115, either by being mountedon the shaft 115 or by another desired and appropriate technique, suchas including the rectifier 115 with the secondary winding of thetransformer 140. If desired, the output of the secondary winding 140Band/or the rectifier 145 may be filtered or smoothed before beingapplied to the rotor 135.

One may also consider the synchronous machine 100 as having a stationarysection 150 and a rotating section 155, the stationary section 150comprising the frame 110, the primary winding 140A, and the stator 130,and the rotating section 155 comprising the shaft 115, the rotor 135,the secondary winding 140B, and the rectifier 145.

The electrical lines 165 connected to the stator 130 serve as inputlines to provide an electrical input voltage and power to thesynchronous machine 100 when operation is in the synchronous motor mode,and serve as output lines to provide an electrical output voltage andpower from the synchronous machine 100 when operation is in thesynchronous generator mode.

A control unit 170 monitors one or more parameters of the electricallines 165 and provides an output control signal over conductors 180 tothe primary winding 140A. The control unit 170 may monitor parameterssuch, as but not limited to, the voltage, current, frequency, and/orphase on the electrical lines 165. The parameters which are monitoredmay depend in part on whether the machine 100 is being operated as amotor or as a generator. These input parameters may be filtered, ifdesired, to reduce noise before they are provided to the control unit170.

The control signal is an alternating waveform voltage (AC voltage) suchas, but not limited to, a pulse width modulated (PWM) AC signal. Thecontrol signal preferably has a rectangular waveform, such as providedby a pulse width modulation switching system, but may be a sinusoidalwaveform, or another desired waveform. The control unit 170 controls atleast one of a pulse width, a voltage (which may be a pulse voltage), ora frequency (which may be a pulse frequency) of the control signal. Thecontrol signal may be a plurality of pulses or a plurality of cycles ofan AC signal, a single pulse or a cycle of an AC signal, a part of acycle of an AC signal, or a combination thereof. For example, dependingupon the monitored input parameters, the control signal may be twopulses or two cycles of an AC signal, may be 6½ pulses or 6½ cycles ofan AC signal, or may be less than a full cycle of an AC signal. Pulsesmay be in sets, with variable lengths, with different numbers indifferent sets, and/or variable spacing between sets. The control signalmay be filtered, if desired, before being provided to the primarywinding 140A.

The control signal is a “high frequency” control signal; that it, it hasa frequency which is higher than the input frequency (motor mode), thatis, the frequency of the input signal on electrical lines 165, andhigher than the output frequency (generator mode), that is, thefrequency of the output signal on electrical lines 165. More preferably,the frequency of the control signal is at least several times higherthan the frequency of the voltage on electrical lines 165. Even morepreferably, the frequency of the control signal is at least 10 times thefrequency of the voltage on electrical lines 165 in order to minimizethe effects on excitation caused by the rotation speed of the rotor 135.Higher frequencies may also be used. Lower frequencies may also be used,but the size, weight, and cost of the windings 140A, 140B may increaseas the frequency is lowered, and coupling between the primary andsecondary windings may become affected by the rotational speed of theshaft. In one implementation, the frequency of the control signalprovided to the transformer 140 is 10 kHz if the frequency of thevoltage on electrical lines 165 is 400 Hz. In addition, the use of sucha higher frequency for the control signal allows the transformer 140 touse smaller windings, and less iron, that the exciter armature windingsof conventional systems.

The control unit 170 may also monitor other parameters or aspects of theoperation of the synchronous machine 100 such as, by way of example andnot of limitation, the rotation speed, the shaft angular position, thechanges therein, etc. For example, a shaft position encoder (not shown)may be connected to the shaft to provide the angular position of theshaft. The control unit 170 may then adjust the control signal onconductors 180 accordingly. For example, if the machine is beingoperated as a motor and the load is such that the changes in the shaftangular position indicate that the motor may not be able to maintainsynchronous operation then the power provided to the primary winding140A, and therefore to the rotor 135, may be increased. As anotherexample, if the machine is being operated as a generator and the outputvoltage on lines 165 is increasing then the power provided to theprimary winding 140A may be decreased. The control unit 170 may vary thepower by adjusting, for example, the pulse width, the pulse repetitionrate, the amplitude of the control signal on conductors 180, and/or thepulse pattern (e.g., how many pulses are provided in a set of pulses,the time between each set of pulses, etc.).

This synchronous machine design provides for the use of a single compacthigh frequency exciter stage 125 for both synchronous motor mode andsynchronous generator mode. As mentioned, the primary winding 140A andthe secondary winding 140B are in a spaced apart relationship; that is,they do not contact each other, and the secondary winding 140B moves asthe shaft 115 rotates whereas the primary winding 140A, mounted to theframe 110, does not move. The control unit 170 provides the highfrequency control signal (input voltage) to the primary winding 140A,which induces a high frequency AC output voltage on the secondarywinding 140B. This high frequency AC output voltage is rectified by therectifier 145 to provide a direct current (DC) to the rotor 135. Therectifier 145 may be, by way of example and not of limitation, afull-wave rectifier or a bridge rectifier.

The high frequency output from the control unit 170 allows for the useof a smaller transformer 140, thereby reducing the size of the excitersection 145 and also reducing copper and iron losses. The high frequencyalso enables a wider control bandwidth, which provides for bettermachine speed stability and better torque control. This single excitersection 145 also provides a simplified machine architecture, reducedweight of copper and/or iron used therein, reduced volume, and reducednumber of excitation sources (smaller component count). This single,high frequency exciter section 145 thereby provides better efficiencyand higher reliability than the conventional systems mentioned above.

As seen from FIG. 1, only one rotor 135 and only one control unit 170are used for both synchronous motor operation and synchronous generatoroperation. Elimination of the duplicate rotors and control units used inconventional designs reduces the volume, weight, and number ofcomponents of the synchronous machine 100.

Further, by using a high frequency AC input voltage to the transformer140, the voltage provided to the rotor 135 is more stable than inconventional synchronous machines. A more stable voltage to the rotor135 improves the stability and control in the process of starting thesynchronous machine 100.

FIG. 2 is a diagram illustrating one exemplary embodiment of thesynchronous machine 100 showing the frame 110, the shaft 115, the stator130, the rotor 135, the transformer windings 140A, 140B, the rectifier145, and the bearings 160A, 160B. Also shown are conductors 180 whichconnect to the primary winding 140A through a hole, grommet, or otheropening 110A, preferably but not necessarily sealed, in the frame 110.Also shown are conductors 137 and 142. For convenience and clarity ofillustration, these conductors 137 and 142 are shown as being apart fromthe shaft 115. In practice, however, these conductors would preferablybe mounted directly to the shaft 115 so as to minimize the centrifugalforces on these conductors. They could also be placed in a groove (notshown) in the shaft. The groove would be as shallow as possible so as tohave the minimum effect on the strength and integrity of the shaft 115.If desired, the conductors 137 and 142 could be placed in a channel inthe shaft 115, such as is shown in FIG. 3.

In the embodiment of FIG. 2, each transformer winding 140A, 140B ispreferably in the shape of a disk, which may have a width, length,depth, wire size, and number of turns as convenient and appropriate fora particular implementation. Primary winding 140A may be considered tobe an “outer” winding, and secondary winding 140B may be considered tobe an “inner” winding. The primary winding 140A has an interior radius140A1 with respect to the centerline 115A of the shaft 115, and thesecondary winding 140B has an exterior radius 140B1 with respect to thecenterline 115A of the shaft 115. The exterior radius 140B1 is less thanthe interior radius 140A1, so that winding 140B is fits inside of and isinterior to winding 140A. The spacing between the windings 140A, 140B issufficiently small that the windings 140A, 140B are magnetically coupledto each other. Preferably, windings 140A and 140B are in substantiallythe same plane 175. Windings 140A and 140B need not be in exactly thesame plane 175, they may be slightly offset from each other. Windings140A and 140B are considered to be in substantially the same plane, evenif offset from each other, if the magnetic coupling between them issufficient to provide the appropriate power and control to the rotor135. The windings 140A and 140B are in a container, such as 140A2 and140B2, respectively, to protect the windings and hold the windings inplace. The containers are preferably made of ferrite or other materialwhich serves to provide a closed path for the magnetic lines of forcefrom the windings and to increase the magnetic coupling between thewindings. The shaft 115 may also serve to concentrate the magnetic fluxand increase coupling if the shaft 115 is made of or includes aferromagnetic material, especially if the containers are not made of amaterial which increases the coupling.

Although the frame 110 is illustrated as being a stepped frame, whereone part of the frame has a different radius than another part of theframe, this is not a requirement; the frame may have a different shape,such as having the same radius throughout its entire length, as shown inFIG. 3. Also, although the frame 110 is illustrated as beingsingle-ended, that is, end 1108 is open and end 110C is closed, so thatthe shaft 115 only extends from end 1108 of the frame, this is not arequirement. The end 110C may also be an open end so that the shaft 115may extend from both end 1108 and end 110C. In addition, although theexciter section 125 is illustrated as being at the closed end 110C ofthe frame 110, it could instead be at the open end 1108 of the frame110.

FIG. 3 is a diagram illustrating another exemplary embodiment of thesynchronous machine 100. In this embodiment transformer windings 140A,140B are not “inner” and “outer” windings, they are parallel or facingwindings but they are not in the same plane. Rather, winding 140A is inplane 175A, and winding 140B is in plane 1758 so that they face eachother. They are again preferably in the shape of a disk. In thisembodiment the conductors 137 from the secondary winding 140B to therectifier 145 are at least partially within a channel or hollow section1158 in the shaft 115 so that the conductors 137 do not interfere withthe bearing 160B.

In an alternative embodiment, the rectifier 145 may be, if desired,positioned outside of the bearing 160B, that is, between the bearing160B and the end 110C. In this alternative embodiment the conductors 137may or may not be in the channel 1158, but the conductors 142 from therectifier 145 to the rotor winding 135 would be at least partiallywithin the channel 115B in the shaft 115 so that the conductors 142 donot interfere with the bearing 160B.

Although the rectifier 145 is shown in FIGS. 2 and 3 as being separatefrom the secondary winding 140B, this is not a requirement. For example,the rectifier 145 could be embedded in or within the container 140B2.

Also, the channel 115B design can be used with the embodiment of FIG. 2if, for example, it is desired that the exciter section 125 be betweenthe bearing 160B and the end 110C.

The embodiment of FIG. 2, in addition to the advantages and benefitsdescribed above, is also advantageous in another respect. If thesynchronous machine 100 is used with, for example, a screw drive, thenthe compressive and tensile forces on the shaft 115 may cause the shaft115 to shift slightly along its length, that is, toward, or away from,an end 1108 or 110C, but a shift will have little effect upon themagnetic coupling between the windings 140A and 140B.

The embodiment of FIG. 3, in addition to the advantages and benefitsdescribed above, is also advantageous in another respect: reducedcentrifugal forces exerted upon the windings 140A and 140B. As thewindings 140A and 140B are closer to the axis 115A, the centrifugalforces exerted upon them will be less than the forces exerted in theembodiment of FIG. 2. This reduction in centrifugal forces may besignificant for a synchronous machine 100 which is to be operated at avery high revolution per minute rate, as might be the case for somesmaller-size synchronous machines.

Thus, the use of a single exciter stage transformer 140, instead of theuse of two separate excitation stage transformers or reconfigurablewindings, reduces the weight of copper and iron in the machine, andreduces the number of switches and contactors required when twotransformers are used. Further, only one exciter source, control unit170, is used, rather than two or more excitation sources. The singlecontrol unit 170 controls the synchronous machine 100 for both motormode and generator mode of operation, simplifies the control design, andreduces the number of components. A high frequency control signal,instead of a low frequency control signal, provides for better control.

A method of operating the synchronous machine as either a synchronousmotor or a synchronous generator includes (1) applying a firstalternating voltage to the primary winding and applying a secondalternating voltage to the stator to cause the synchronous machine tooperate as a synchronous motor providing an output torque, or (2)applying a first alternating voltage to the primary winding and applyingan input torque to the shaft to cause the synchronous machine to operateas a synchronous generator to provide an output voltage. At least one ofa voltage, a frequency, or a duty cycle of the first alternating voltageis adjusted to control an output torque when operating the synchronousmachine as a synchronous motor or an output voltage when operating thesynchronous machine as a synchronous generator.

“About”, “approximately”, “substantially”, and similar terms, as may beused herein, are relative terms and indicate that, although two valuesmay not be identical, their difference is such that the apparatus ormethod still provides the indicated or desired result, or that theoperation of a device or method is not adversely affected to the pointwhere it cannot perform its intended purpose.

The subject matter described herein is provided by way of illustrationfor the purposes of teaching, suggesting, and describing, and notlimiting or restricting. Combinations and alternatives to theillustrated embodiments are contemplated, described herein, and setforth in the claims. Various modifications and changes may be made tothe subject matter described herein without strictly following theembodiments and applications illustrated and described, and withoutdeparting from the scope of the following claims.

The subject matter described above is provided by way of illustrationonly and are not to be construed as limiting. Various modifications andchanges may be made to the subject matter described herein withoutfollowing the exemplary embodiments and applications illustrated anddescribed herein. Although the subject matter presented herein has beendescribed in language specific to components, features, and operations,it is to be understood that the appended claims are not necessarilylimited to the specific components, features, or operations describedherein. Rather, the specific components, features, and operations aredisclosed as example forms of implementing the claims.

1. A synchronous machine comprising: a frame; a shaft extending from atleast one end of the frame and having a channel formed therein; a mainsection, comprising: a stationary winding mounted to the frame; and arotating winding, mounted on the shaft, and spaced apart from, andmagnetically coupled to, the stationary winding; and an exciter section,comprising: a transformer having a primary winding and a secondarywinding spaced apart from, and magnetically coupled to, each other, eachwinding being in the shape of a disk, the primary winding being mountedto the frame at an end of the shaft, the disk of the primary windingdefining a first plane which is perpendicular to the shaft, thesecondary winding being secured to the shaft near an end of the shaft,the disk of the secondary winding defining a second plane which isperpendicular to the shaft, the second plane being parallel to andspaced apart from the first plane, the shaft not penetrating the firstplane; a rectifier, mounted on the shaft, to rectify an output of thesecondary winding and provide a rectified output to the rotatingwinding; first conductors to electrically connect the rectified outputof the rectifier to the rotating winding; and second conductors toelectrically connect the output of the secondary winding to therectifier; wherein at least part of the first conductors or at leastpart of the second conductors are within the channel of the shaft. 2.The synchronous machine of claim 1, further comprising: a control unitconfigured to provide a control signal to the primary winding.
 3. Thesynchronous machine of claim 1, wherein the stationary winding is afield winding, and wherein the rotating winding is an armature winding.4. The synchronous machine of claim 1, wherein the synchronous machineoperates as a synchronous generator when an input torque is applied tothe shaft.
 5. The synchronous machine of claim 1, wherein thesynchronous machine operates as a synchronous motor when an inputvoltage is applied to the stationary winding.
 6. The synchronous machineof claim 1, further comprising: a control unit configured to provide acontrol signal to the primary winding, wherein the control unit variesat least one of a duty cycle, a frequency, or an output voltage of thecontrol signal.
 7. The synchronous machine of claim 1, furthercomprising: a control unit to provide a control signal to the primarywinding, wherein the synchronous machine operates as a synchronousgenerator providing an output voltage having an output frequency when aninput torque is applied to the shaft, and wherein the control unitcauses the control signal to have a frequency at least several timeshigher than the output frequency of the output voltage.
 8. Thesynchronous machine of claim 1, further comprising: a control unit toprovide a control signal to the primary winding, wherein the synchronousmachine operates as a synchronous motor when an input voltage having aninput frequency is applied to the stationary winding; and wherein thecontrol unit causes the control signal to have a frequency at leastseveral times higher than the input frequency of the input voltage. 9.The synchronous machine of claim 1, wherein at least part of the firstconductors are within the channel of the shaft.
 10. The synchronousmachine of claim 1, wherein the transformer further comprises: a firstcontainer mounted to the frame, wherein the primary winding is disposedin the first container; and a second container secured to the shaft nearthe end of the shaft, wherein the secondary winding is disposed in thesecond container.
 11. The synchronous machine of claim 10, wherein thesecond container and the shaft are coaxially arranged.
 12. Thesynchronous machine of claim 11, wherein the second container is securedto an endface of the shaft.
 13. A method of manufacturing a synchronousmachine operable as either a synchronous motor or a synchronousgenerator, the method comprising: providing a frame; mounting astationary winding to the frame; providing a shaft which extends from atleast one end of the frame; mounting a rotating winding on the shaft,the rotating winding being spaced apart from, and magnetically coupledto, the stationary winding; mounting a primary winding of a transformeron the frame, wherein the primary winding is formed as a disk defining afirst plane, wherein the shaft does not intersect the first plane;mounting a secondary winding of the transformer to an end of the shaft,wherein the secondary winding is spaced apart from, and magneticallycoupled to, the primary winding, wherein the second winding is formed asa disk defining a second plane that is parallel to the first plane;securing a rectifier to the shaft; connecting an input of the rectifierto the secondary winding; and connecting an output of the rectifier tothe rotating winding.
 14. The method of claim 13, wherein the shaft hasa channel, and wherein the secondary winding is connected to therectifier by placing conductors in the channel.
 15. A synchronousmachine comprising: a rotatable shaft; a main section comprising: arotating winding mounted to the rotatable shaft; and a stationarywinding spaced apart from, and magnetically coupled to, the rotatingwinding; and an exciter section comprising: a primary transformerwinding arranged near an end of the rotatable shaft, wherein the primarytransformer winding is in a first plane that is perpendicular to an axisof the rotatable shaft, wherein the first plane and the rotatable shaftare non-intersecting; a secondary transformer winding secured to therotatable shaft near the end, wherein the secondary transformer is in asecond plane that is parallel to the first plane; and a rectifiermounted to the rotatable shaft, wherein an input of the rectifier iscoupled to the secondary transformer winding, and wherein an output ofthe rectifier is coupled to the rotating winding.
 16. The synchronousmachine of claim 15, wherein a channel is formed in the rotatable shaft,and wherein one or more electrical conductors coupled with the rectifierextend through the channel.
 17. The synchronous machine of claim 15,wherein the rotatable shaft extends from at least one end of a frame,and wherein the primary transformer winding is mounted to the frame. 18.The synchronous machine of claim 17, wherein the primary transformerwinding is disposed in a first container mounted to the frame, andwherein the secondary transformer winding is disposed in a secondcontainer secured to the rotatable shaft near the end.
 19. Thesynchronous machine of claim 18, wherein the second container and theshaft are coaxially arranged.
 20. The synchronous machine of claim 18,wherein the second container is secured to an endface of the shaft.